Method for determining a hot-start situation in an internal combustion engine

ABSTRACT

A method for detecting a hot start situation in an internal combustion of a motor vehicle includes the steps of determining a gradient of a temperature variation of an engine temperature; and detecting a hot start situation based on the determined gradient of a temperature variation of an engine temperature. An appropriate electronic control unit for an internal combustion engine is provided, as well as an appropriate computer program with a program code mechanism, and an appropriate computer program product with a program code mechanism.

BACKGROUND OF THE INVENTION

The invention concerns a method for detecting a hot start situation inan internal combustion engine of a motor vehicle. The invention alsoconcerns an appropriate electronic control unit for an internalcombustion engine, an appropriate computer program with program codemeans, and an appropriate computer program product with program codemeans.

In general, a hot start situation exists, e.g., when an internalcombustion engine that is still hot is restarted after a short pause inoperation. When a hot machine is at rest, fuel vapor bubbles form in thefuel lines and in the injection valve itself. When said machine is thenstarted, these fuel vapor bubbles inhibit regular fuel metering. Forthis reason, an extended injection signal is output under hot startconditions, so that a certain minimum amount of fuel can be provided tothe combustion process even when fuel vapor bubbles occur. It istherefore necessary to determine when a hot start situation exists.

Publication DE 40 39 598 A1 discloses a hot start method and a hot startdevice for an internal combustion engine. According to the teachingdisclosed in said publication, a hot start situation is assumed to existwhen the engine temperature and the air intake temperature exceedcertain threshold values and, moreover, the absolute-value differencebetween the air intake temperature at an earlier point in time and theair intake temperature during restart is above a selectable threshold.

Publication DE 44 35 419 A1 discloses a control system for the fuelmetering of an internal combustion engine. In this case, a hot startsituation is assumed to exist and an appropriate hot start bit is setwhen the temperature of the internal combustion engine exceeds aninitial threshold and, in addition to this, the air intake temperaturehas increased by a certain amount since a last measurement. The lastvalue can be the one that existed at the instant when the internalcombustion engine was shut down, and the new value can have beenobtained at the instant when the ignition or the starter was switchedon. The hot start bit remains set until the internal combustion enginetemperature exceeds a second threshold, or until a predetermined totalair mass has flowed through the intake manifold. Said total air mass isdetected by integrating the signal of an air mass sensor in the intakemanifold.

In the case of modern fuel injection systems that operate withhigh-pressure fuel injection in particular, some components, e.g., thehigh-pressure pump, heat up substantially slower than the coolant of theinternal combustion engine. It is therefore possible, after the internalcombustion engine has been shut off, for the coolant temperature to havealready dropped or to drop compared to the shut-off temperature, whilethe temperature of the high-pressure pump and other components is stillhigh and/or increases even further.

SUMMARY OF THE INVENTION

The invention is based on the object of improving a method for detectinga hot start situation in an internal combustion engine of a motorvehicle, and for improving a control element. This object is attained bymeans of the features characterized in the independent claims.Advantageous and necessary embodiments and further developments of theinvention are characterized in the dependent claims.

A method for determining a hot start situation in an internal combustionengine of a motor vehicle is developed further compared to the relatedart in that a hot start situation is detected at least based on agradient and/or a temperature rise of a temperature variation of anengine temperature. By evaluating the temperature variation, a furthertemperature variation of the internal combustion engine can be diagnosedfurther in particularly advantageous fashion. The detection of a hotstart situation is advantageously carried out based on the temperaturevariation between shut-off and restart of the internal combustionengine. The advantageous further development provides that the detectiontakes place during an electronic control unit tracking after theinternal combustion engine is shut off. By means of this furtherdevelopment, a temperature variation of the internal combustion enginecan be detected in a particularly reliable and technically simplefashion. The duration of the electronic control unit tracking must beselected so that is ensures that the temperature variation can beanalyzed for an adequately long period of time. Advantageously, theengine temperature is detected based on a coolant temperature and/or anair intake temperature and/or a temperature of a temperature sensor inthe engine compartment of the motor vehicle. It is particularlyadvantageous to evaluate the coolant temperature, i.e., usually thecooling water temperature, in particular, because the temperature can bedetected by means of a temperature sensor that is located in the coolantcircuit of the motor vehicle anyway, and an additional temperaturesensor can therefore be eliminated.

A further development provides that, as further criteria for a hot startsituation, at least the engine temperature and/or an air intaketemperature must be greater than an applicable threshold. Due to thisadditional criterium, the reliability of the method according to theinvention is markedly improved once more. It is also provided that, todetect a hot start situation, the gradient and/or the temperature riseof the temperature fluctuation of the engine temperature must be greaterthan an applicable threshold. By using applicable threshold values, themethod according to the invention can be adapted in particularlyadvantageous fashion to various types of motor vehicles with differentinternal combustion engines. It can be adapted for use withdiesel-powered as well as gasoline-powered internal combustion engines.

A particularly preferred further development provides that thedimensions of the applicable thresholds are designed to ensure that anelevated temperature of a high-pressure fuel pump located in thecombustion chamber is detected. This embodiment is particularlyadvantageous in modern internal combustion engines with high-pressurefuel injection. An internal combustion engine with gasoline directinjection that is described in the exemplary embodiment of the inventionis particularly worth mentioning here.

Another further development provides that an independent method fordetecting a hot start situation is carried out simultaneously, and a hotstart situation is detected when one of the two methods detects a hotstart situation. A difference between an air intake temperature when theinternal combustion engine is shut off and when it is started, and anengine temperature threshold can be used advantageously as the criteriumin this case. A method such as this that is carried out in parallel canbe performed using DE 44 35 419 A1 mentioned hereinabove, for example.

Another preferred further development is based on the fact that thetemperature rise is the difference between the maximum temperatureduring the electronic control unit tracking and a shut-off temperatureof the internal combustion engine, and that the gradient is calculatedbased on the temperature variation during the electronic control unittracking. In this manner, the criteria for detecting a hot start thatare relevant for evaluation purposes can be determined during electroniccontrol unit tracking.

Of particular significance is the realization of the method, accordingto the invention, in the form of an electronic control unit for aninternal combustion engine, in particular of a motor vehicle. Means forcarrying out the steps of the method described hereinabove are provided.

Of particular significance, furthermore, are the realizations in theform of a computer program with program code means and in the form of acomputer program product with program code means. The computer programaccording to the invention comprises program code means in order tocarry out all steps of the method according to the invention when theprogram is run on a computer, in particular an electronic control unitfor an internal combustion engine of a motor vehicle. In this case, theinvention is therefore realized by means of a program stored in theelectronic control unit, so that this electronic control unit equippedwith the program represents the invention in the same fashion as themethod, the execution of which the program is suited for. The computerprogram product according to the invention comprises program code meansthat are saved on a computer-readable data storage medium in order tocarry out the method according to the invention when the program productis carried out on a computer, in particular an electronic control unitfor an internal combustion engine of a motor vehicle. In this case, theinvention is therefore realized by means of a data storage medium, sothat the method according to the invention can be carried out when theprogram product and/or the data storage medium is integrated in anelectronic control unit for an internal combustion engine of a motorvehicle, in particular. An electrical storage medium can be used inparticular as data storage medium and/or as computer program product,e.g., a Read-Only-Memory (ROM), an EPROM, or an electrical, non-volatilememory such as a CD-ROM or a DVD.

Further features, possibilities for use and advantages of the inventionresult from the following description of exemplary embodiments of theinvention that are shown in the figures below. All described orillustrated features—alone or in any combination—represent the object ofthe invention, independent of their summarization in the claims or theirbackward reference, and independent of their formulation and/or theirdepiction in the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained hereinbelow with reference to anexemplary embodiment shown in the figures. FIG. 1 shows an exemplaryembodiment of the method according to the invention, and FIG. 2 shows anillustration of measured values when the method according to theinvention is carried out.

FIG. 1 shows an exemplary embodiment of the method according to theinvention for detecting a hot start situation in an internal combustionengine of a motor vehicle. In a Step 101, the internal combustion engineof the motor vehicle is in a normal engine operating mode to start with.In other words: The motor vehicle and/or the internal combustion engineis running and a normal operating sequence is taking place. In Step 102,it is assumed that the driver of the motor vehicle intends to switch theinternal combustion engine off. This can take place by turning theignition key, for example. At this instant, the current engine shut-offtemperature tmotab is saved in Step 102. In this exemplary embodiment,the engine shut-off temperature tmotab corresponds to the temperature ofthe cooling water temperature tmot determined by the cooling-watersensor. In Step 103, the engine and/or the internal combustion engine ofthe motor vehicle is shut off. In Step 104, according to the invention,the further cooling water temperature variation tmot is consideredduring electronic control unit tracking. To accomplish this, the maximumengine temperature tmotmax and the maximum gradient tmotgradmax of theengine temperature and/or, in this exemplary embodiment, of the coolingwater temperature, is determined and stored, in Step 105 it is assumedthat the drive of the motor vehicle wants to restart the internalcombustion engine. To accomplish this, the electronic control unit ofthe internal combustion engine is initialized before the restart. Afterinitialization of the electronic control unit before restart in Step105, the temperature difference between the maximum engine temperaturetmotmax during the electronic control unit tracking after the engine isshut off, and the engine shut-off temperature from Step 102 is firstcalculated in Step 106. Furthermore, a check is performed in Step 106 todetermine if this temperature difference between tmotmax and tmotab isgreater than an applicable, temperature-dependent threshold, or whetherthe maximum gradient of the engine temperature tmotgradmax determinedduring the electronic control unit tracking is greater than anapplicable temperature-dependent threshold. If it is determined thatnone of the threshold values is exceeded, the process jumps to Step 107,in which a conventional hot start detection is carried out in addition.A conventional hot start detection of this nature can take place, forexample, in analogous fashion to that described in the introduction tothe description in DE 44 35 419 A1. If a hot start is not detected inStep 107 in this hot start detection, either, the process jumps to Step108, in which it is determined once and for all that a hot startsituation does not exist. In Step 109, the method according to theinvention for determining a hot start situation is completed. Thecorresponding setting parameters of the internal combustion engine arechanged depending on whether or not a hot start situation was detected.

If it was determined in Step 106 that one or two of thetemperature-dependent threshold values was exceeded, the process jumpsto Step 110. In Step 110, a check is now performed to determine ifeither the engine temperature and/or the air intake temperature exceedan applicable threshold value. If this is not the case, the processjumps to Step 108 and it is determined that a hot start situation doesnot exist. This is the case when, immediately after the motor vehicle isshut off, for example, a high maximum temperature value tmotmax and,therefore, a high temperature rise (tmotmax-tmotab) and/or a maximumtemperature gradient of the engine temperature tmotgradmax is determinedduring the electronic control unit tracking, but the vehicle cansubsequently cool down long enough for the engine temperature and theair intake temperature to fall below the predetermined threshold values.

If, on the other hand, it is determined in Step 110 that the enginetemperature and/or the air intake temperature are above applicablethreshold values, it is determined that a hot start situation exists andthe procedure continues at Step 111. In Step 111, it is determined thata hot start situation exists. In this context, an appropriate hot startbit can be set in the electronic control unit, for example. In the nextStep 109, the method, according to the invention, for determining a hotstart situation ends, and the internal combustion engine is started withthe appropriate parameters for a hot start situation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

If a hot start situation was detected in Step 107, the process jumpsinitially to Step 110 by comparing the engine temperature and air intaketemperature values with corresponding threshold values. If it is therebydetermined that the engine temperature and air intake temperature valuesare below applicable threshold values, a final decision is made in Step108 that a hot start situation does not exist, despite the fact that ahot start situation was detected in Step 107.

FIG. 2 shows a depiction of measured values when the method according tothe invention is carried out. FIG. 2 shows rotational speed andtemperature data plotted over time. A characteristic 21 shows therotational-speed variation nmot of an internal combustion engine. It isobvious that the rotational speed 21 drops sharply to 0 after a shortperiod of time at a relatively high, constant rotational-speed value andthen remains at 0. This instant when the rotational speed drops offsharply corresponds with the shutting-off of the internal combustionengine. The characteristic 22 represents the measured variation incooling water temperature tmot of the internal combustion engine. Alsoshown in FIG. 2 is a characteristic 23 that corresponds to the measuredtemperature of a high-pressure pump in an internal combustion enginewith gasoline direct injection. Also shown is the temperature threshold24 that corresponds to the shut-off temperature tmotab of the internalcombustion engine, and the temperature threshold 25 that corresponds tothe maximum temperature tmotmax during the electronic control unittracking.

It is obvious that the course of the cooling-water temperature 22initially increases sharply to a maximum value 25 after the internalcombustion engine is shut off, and then drops off steadily. The steeprise in the temperature variation of the cooling water temperature 22that occurs during the electronic control unit tracking is approximatedby a maximum temperature gradient tmotgradmax, shown as line 26. Inaddition, the maximum temperature rise 27 occurs between the shut-offtemperature 24 (tmotab) and the maximum temperature during theelectronic control unit tracking 25 (tmotmax). The method according tothe invention for detecting a hot start situation is essentially basedon the fact that a check is performed to determine whether the maximumtemperature gradient 26 (tmotgradmax) or the maximum temperature rise 27(tmotmax-tmotab) are above applicable threshold values.

The characteristic 23, which corresponds to the temperature of ahigh-pressure pump of a fuel supply system, shows clearly how thetemperature of the high-pressure pump continues to increase after themotor vehicle is shut off. In theory, the temperature of thehigh-pressure pump 23 can climb to the temperature of the cooling watervariation 23 at the maximum. As time progresses, it is obvious in FIG. 2that the temperature variations 22 and 23 approach each other. Line 28represents a temperature threshold that is a limit temperature of thehigh-pressure pump, at which a hot start situation is given for thehigh-pressure pump. In other words: Starting at this temperaturethreshold 28, the high-pressure pump reaches a temperature at which theinternal combustion engine can no longer be properly supplied with fueldue to vapor bubbles forming in the fuel. Starting at instant t1,therefore, which is indicated by a vertical line, a hot start situationfor the internal combustion engine with gasoline direct injection isgiven by the fact that the high-pressure pump has exceeded the hot startlimit temperature for the high-pressure pump 28.

It is precisely this critical temperature rise of the high-pressure pumpthat can be detected according to the invention by means of thedetermined temperature gradient tmotgradmax and/or the determinedmaximum temperature rise (tmotmax-tmotab). Measurements have shown thata hot start situation—indicated by an overheated high-pressure pump—canbe reliably determined using the method according to the invention.

The electronic control unit tracking required to carry out the methodaccording to the invention takes approximately two minutes to movethrough the measured values shown in FIG. 2.

1. A method of detecting a hot start situation in an internal combustionengine of a motor vehicle, comprising the steps of determining agradient of a temperature variation of an engine temperature; anddetecting a hot start situation based on the determined gradient of atemperature variation of an engine temperature.
 2. A method as definedin claim 1; and further comprising carrying out the detection based onthe temperature variation between a shut-off and a renewed starting ofthe internal combustion engine.
 3. A method as defined in claim 2; andfurther comprising carrying out the detection during an electroniccontrol unit tracking after the internal combustion engine is shut down.4. A method as defined in claim 1; and further comprising detecting anengine temperature based on a parameter selected from the groupconsisting of a coolant temperature, an intake air temperature, atemperature of a temperature sensor in an engine compartment of themotor vehicle, and a combination thereof.
 5. A method as defined inclaim 1; and further comprising using as a further criteria for a hotstart situation at least one parameter selected from the groupconsisting of an engine temperature, an air intake temperature, and acombination thereof, which parameter must be greater than an applicablethreshold.
 6. A method as defined in claim 1; and further comprisingusing, to detect a hot start situation, using a parameters selected fromthe group consisting of an engine temperature, an air intaketemperature, and a combination thereof, which parameter must be greaterthan an applicable threshold.
 7. A method as defined in claim 1; andfurther comprising carrying out the detection of the hot start situationin a direct-injection gasoline-powered internal combustion engine.
 8. Amethod as defined in claim 1; and further comprising carrying out anadditional, independent method for detecting a hot start situationsimultaneously; and detecting a hot start situation when one of the twomethods detects a hot start situation.
 9. A method as defined in claim8, and further comprising detecting with the additional method a hotstart situation at least based on a difference between intaketemperature when the internal combustion engine is shut down and whenthe engine is started and based on an engine temperature threshold. 10.A method as defined in claim 3; and further comprising considering atemperature rise as a difference between a maximum temperature during anelectronic control unit-tracking and a shut-off temperature of theinternal combustion engine; and calculating the gradient based on thetemperature variation during the electronic control unit-tracking. 11.An electronic control unit for an internal combustion engine of a motorvehicle for detecting a hot start situation in the internal combustionengine, comprising means for determining a gradient of a temperaturevariation of an engine temperature; and means for detecting a hot startsituation at least based on the determined gradient of a temperaturevariation of an engine temperature.
 12. A computer program with programcode means to carry out a method of detecting a hot start situation inan internal combustion engine of a motor vehicle, comprising the stepsof determining a gradient of a temperature variation of an enginetemperature; and detecting a hot start situation based on the determinedgradient of a temperature variation of an engine temperature, whereinthe program is carried out on a computer in an electronic control unitfor an internal combustion engine.
 13. A computer program product withprogram code means that are stored on a computer-readable data storagemedium to carry out a method of detecting a hot start situation in aninternal combustion engine of a motor vehicle, comprising the steps ofdetermining a gradient of a temperature variation of an enginetemperature; and detecting a hot start situation based on the determinedgradient of a temperature variation of an engine temperature, whereinthe program is carried out on a computer in an electronic control unitfor an internal combustion engine.
 14. A method as defined in claim 1,wherein said detecting a hot start situation is based at least on agradient and a temperature rise of a temperature variation of an enginetemperature.